As is known in the art, a radio frequency (RF) transmitter is a device that produces RF signals. RF transmitters may be included, for example, as part of a radio communication system that uses electromagnetic waves (radio waves) to transport information over a distance.
As is also known, a trade-off must generally be made in RF communications transmitters between energy efficiency and linearity. Over the decades of development of the RF transmitter and corresponding RF amplifiers, it has generally been true that one could obtain either high efficiency or high linearity, but not both. It would, therefore, be desirable to provide systems and techniques that allow a user to amplify RF signals and/or transmit data carrying RF signals with both high efficiency and high linearity.
U.S. Pat. No. 8,824,978, which is herein incorporated by reference in its entirety, describes a transmitter amplifier architecture (referred to herein as the “Asymmetric Multilevel Backoff Amplifier” or “AMBO amplifier”) that has provides high efficiency operation at wide radio-frequency (RF) bandwidth with high linearity, efficient operation under power backoff, in addition to other advantages.
An AMBO amplifier may have plurality of RF power amplifiers (PAs) whose RF outputs are power combined to supply a system RF output, and whose PA drain bias voltages may be dynamically selected using voltage control units.
In known AMBO amplifiers, one way to drive the RF inputs of the PAs is for a controller to synthesize a digital command (e.g., an I/Q signal pair) for each PA. The digital commands are converted, through the use of two or more digital-to-RF modulators, into RF input signals for the PAs. By coordinating the switching of the PA drain bias voltages and the RF input commands to the PAs, an RF output can be generated that accurately reflects a desired digital I/Q input while preserving high efficiency and linearity at high bandwidth and across a wide range of power levels. This implementation of AMBO with multiple digital-to-RF conversion paths is referred to herein as “dual-digital” AMBO.